Radio Frequency identification (RFID) systems are used for identification and/or tracking of equipment or inventory such as pallets, trucks, dollies or boxes or even the whereabouts of some animals, such as livestock in certain situations. These RFID systems are radio communication systems in which communications is provided between a radio transceiver, or interrogator, and a number of small, identifying labels or tags. These tags are read while in the radiation pattern or field of the interrogator, which may be connected to a computer-based tracking system. The intent of an RFID system is to provide a reliable and secure architecture that meets a predetermined performance requirement, while minimizing the cost of the interrogator and the tags. In the operation of RFID systems, the interrogator transmits to the tags using modulated radio signals, and the tags respond by transmitting modulated radio signals back to the interrogator. Specifically, the interrogator first transmits an amplitude modulated signal to the tag. Next, the interrogator transmits a continuous-wave (CW) radio signal to the tag. The tag then modulates the CW signal using modulated back scattering (MBS) wherein the antenna is electrically switched, by the tag's modulating signal, from being an absorber of radio frequency (RF) radiation to being a reflector of RF radiation; thereby encoding the tag's information onto the CW radio signal. The interrogator demodulates the incoming modulated radio signal and decodes the tag's information message.
Radio frequency identification tags may be used in many applications where messages must be exchanged between the interrogator and the tags. Some applications may employ tags in which the tags are needed for only for a short period of time. These tags may be simple and need to contain only a small amount of information. An example of where such a tag would have application is as a luggage tag that is used in both airline and rail transportation, where a trip is usually completed in less than 48 hours. The use of radio frequency identification tags for this application would increase the efficiency of the check in and passenger-luggage reconciliation process for the airline and the passengers. Such tags, however, must be reliable and secure, yet inexpensive.